Tuesday, August 6, 2013

Scientists assert there is less global weather variability than most people believe

Environment & Energy reports on the Nature paper we highlighted 2 weeks ago finding no increase of climate variability over the past 50 years. According to the authors, "Our findings contradict the view that a warming world will automatically be one of more overall climatic variation" and "Evidence from Greenland ice cores shows that year-to-year temperature variability was probably higher in some past cold periods." Furthermore, the paper finds, "Many climate models predict that total variability will ultimately decrease under high greenhouse gas concentrations..." The paper corroborates other peer-reviewed papers, the IPCC SREX Report, and the Congressional testimony of Dr. Roger Pielke, Jr. & Dr. John Christy finding no evidence of any increase of extreme weather or climate variability with global warming.

Climate change is a broad and complicated topic, often too complicated for the average person. Instead, most of us get our grasp of climate change by looking out the window or stepping out the front door.

It explains why many people in North America and Europe -- recent victims of sweltering heat waves, droughts, floods and other extreme weather events -- believe climate change is causing ever more drastic weather extremes (ClimateWire, July 24).

That may not be the case around the world, however, according to a recent study by a team of British scientists published in the journal Nature. While regions like North America and Europe have been experiencing greater temperature variability, wild shifts from extreme heat to extreme cold, some parts of the world have been seeing more consistent temperatures.

When taken as a whole, global temperature variability has been nearly constant over the last 50 years, according to Chris Huntingford, lead author of the study and a climate modeler at the U.K. Centre for Ecology and Hydrology, part of Britain's government-funded Natural Environment Research Council.

"The general view of the scientific community is that there will be parts of the world where variability does go down, so to colleagues this is not necessarily a complete surprise," he said. Still, changing climate variability is a complicated and hotly debated subject, and Huntingford said the study was simply for "show and tell" purposes conveying their modeling results.

The study, which calculated the range of average global temperature by year using 50 years of data, nevertheless sparked a ripple of discussion through the scientific community. Jennifer Francis, a research professor at the Institute of Marine and Coastal Sciences at Rutgers University, discussed the paper with a group of other scientists shortly after it was released.

Francis said she thought the title of the study, "No increase in global temperature variability despite changing regional patterns," was "kind of misleading." By looking only at annual temperature differences, she said, the study didn't account for smaller-scale variability relevant to sudden and short-lived extreme weather events.

The study "smooths out a lot of variability that's really relevant for extreme weather events and the kind of changes and patterns that have been happening lately," Francis said.

Misperception in the media

The study doesn't ignore regional variability, said James Screen, a research fellow at the University of Exeter who was not involved in the study. He added that people tend to ignore global variability trends in favor of their local experiences. "There's always a bias towards the regions where people live and where events happen, and they cause massive economic losses and hardship to people," he said.

The study noted that the greatest recent year-to-year changes have occurred in much of North America and Europe, something confirmed by a separate study last year. The result, according to several scientists, is a misperception across the West that the weather extremes occurring there are occurring everywhere.

According to Gavin Schmidt, a climate modeler for the NASA Goddard Institute for Space Studies, that misperception makes the study's findings "not a particularly dramatic result."

"General statements about extremes are almost nowhere to be found in the literature but seem to abound in the popular media," Schmidt said. "It's this popular perception that global warming means all extremes have to increase all the time, even though if anyone thinks about that for 10 seconds they realize that's nonsense."

What has managed to avoid attention so far is the decrease in climate variability in the tropics, something scientists have been aware of for a while, according to Francis. "As the world warms up in the future, the tropics are basically going to expand, so the fact that they're becoming less variable, I think, is really a reflection of that," she said.

Variability may decrease as world warms

Huntingford and his co-authors do identify one global trend in climate variability likely to pick up speed: a decrease in annual temperature variability. They write that there is already observational evidence that such variability is now decreasing in Europe and North America as the regions overall become warmer.

"If you were in a warming world," Huntingford said, "the years regarded as extreme could definitely become more routine." They suggested -- cautiously, according to Huntingford -- that rapid sea ice melt in the Arctic is one possible driver behind this future decreased variability.

Recent research suggests melting sea ice has been contributing to extreme weather, but as more sea ice melts in warmer months, the variability it provokes could slowly plateau. "We were given the opportunity by Nature to write a speculative last paragraph, and we think that sea ice probably has a major role in this," Huntingford said.

He added, however, that "the [climate] drivers into the future is something that will require a lot more research." Francis expressed a similar sentiment, arguing that many other factors could be contributing to a decreasing variability. "The fact that both basically are steadily changing doesn't mean that they're connected. There are a lot of things in the climate system that are steadily changing," she said.